Investigation of the number of indoor heatstroke cases by perception time and quantitative evaluation of the effect of air conditioner use on reducing the severity of indoor heatstroke

The number of indoor heatstroke cases aged 60 years or older categorized the "Residential" in the ambulance transport data was aggregated by perception time to investigate the characteristics of temporal changes in the number of indoor heatstroke cases based on the operation status of air conditioner. Simultaneously, association between the severity of indoor heatstroke, categorized as "mild" and "moderate or severe" and use of air conditioner was investigated using the ambulance transport data (June to October 2013 - 2019) provided by the Toyohashi Fire Department, Aichi Prefecture, Japan. The obtained results showed that 1) the number of ambulance transports due to indoor heatstroke, in which the air conditioner was recorded as "OFF" in the transport data, was found to increase sharply from 7:00 a.m., peaking at 9:00 a.m. and 1:00 p.m. Moreover, more patients were diagnosed with "moderate or severe" in the morning than in the afternoon. The high number of cases of indoor heatstroke in the morning was attributed to the possibility of heatstroke occurring during the night or while sleeping, as well as to the delay in calling for emergency medical services. 2) There was a significant association between air conditioner operation status and severity of indoor heatstroke. The use of air conditioner may reduce the probability of moderate or severe heatstroke by an average of 26 points compared to when the air conditioner was OFF.